1. Technical Field
The invention relates to a sliding element, in particular a piston ring, having a coating on at least one running surface.
2. Related Art
Sliding elements such as, for example, piston rings, pistons or cylinder sleeves in internal combustion engines must work over a long service life, both with as little friction as possible and with only a low level of wear. It is the case that the friction, which is directly associated with the fuel consumption in the case of internal combustion engines, can be kept to a low level by coatings of DLC (diamond-like carbon). Further, layer thicknesses of up to 40 μm can be achieved in principle. Nevertheless, in the case of layer thicknesses of more than 5 μm, there is the problem that the layer properties alter, for example in respect of the structure and composition of the layer, such that the required service life is not achieved. This applies likewise to layer thickness of less than 5 μm.
Also known in this connection are PVD coatings based on a hard material, which comprise at least chromium nitride. Although such layers do have the necessary resistance to wear, they nevertheless do not have the required low coefficients of friction.
A sliding element having a DLC coating with a good running-in behaviour is known from DE 10 2005 063 123 B3. Overall, however, the durability of a low coefficient of friction could be improved further.
DE 10 2008 016 864 relates to a sliding element having a coating that comprises, from the inside outwards, an adhesive layer, a metal-containing DLC layer, and a metal-free DLC layer.
DE 197 35 962 A1 discloses a guide bush and a method for realising a hard carbon film on the inner surface of the guide bush, wherein a plasma CVD process is used to realise a hard carbon film of hydrogenated amorphous carbon on the inner surface.
Finally, WO 2006/125683 A1 discloses a piston ring comprising, from the inside outwards, a layer comprising an element of the groups IVB, VB or VIB, an intermediate layer comprising a diamond-like nanocomposite composition, and a DLC layer.